[headshot4444] Java calculator operator parsing

[nerdtopia]

Since headshot4444's inbox is full I'll answer his question here, hopefully it will help someone else too.

Hey I heard you saying you're pretty good with a java. I'm a beginner and stuck on something. I'm trying to read in an operator from an input file. Operators such as "+ - * /". Any good idea on how to read them in? Right now I read them in as strings, and use String.equals("+"), or whatever the operator may be, to determine which operator it is. Thanks.

Sorry for the late response, I don't really check my messages.

Well you could compare as a char :P It really depends on what the input from the file looks like. If the file says something like the following you can use an infix expression algorithm.

Infix:

13*37

or

13 * 37

Postfix:

13 37 *

<strike>I could go into the best way to do this but it requires data structures you probably haven't learned yet (regex string splitting, stack) but the best way to do it (without your teacher accusing you of cheating) goes something like this:</strike> Only answering your question (without your teacher accusing you of cheating) and not writing the entire calculator for you. :P

switch (in.read()) { //InputStream#read() reads a single int from the input stream
            case '+':
                //add
                break;
            case '-':
                //subtract
                break;
            case '*':
                //multiply
                break;
            case '/':
                //divide
                break;
            default:
                //invalid input
                //break; //break; isn't actually required here because the code will continue execution at the same place because it's the last case in the switch. If it wasn't the last case then without the break; the switch would fall through to the next case in the switch.
}

[buyingrafwow]

switch (in.read()) { //InputStream#read() reads a single int from the input stream
            case '+':
                //add
                break;
            case '-':
                //subtract
                break;
            case '*':
                //multiply
                break;
            case '/':
                //divide
                break;
            default:
                //invalid input
                //break; //break; isn't actually required here because the code will continue execution at the same place because it's the last case in the switch. If it wasn't the last case then without the break; the switch would fall through to the next case in the switch.
}

Not sure what he asked for. Reading code from a file and doing math on it?

Because if that's so, I believe you would need to read each line of the file directly, convert them to ints, then create a seperator and finally, read the lines as this:

37 * 12

The * would be the seperator, and you would read on the sides of it, then use the *, etc., in a switch statement/case and have it do the math.

[abuckau907]

@buying That doesn't make sense?? Read each line from file..that makes sense. Convert each one (line?) to an int? How do you convert a line of string to int ?!

*The post question was way too vague ...it all depends on the format ur storing in the txt file..how complicated the equations are (multiple math symbols per line), etc. The problem space wasn't defined well enough. As far as answering his specific question, @nerd answered it just fine with a switch statement.